Enzymes are proteins which act as biological catalysts. It is a substance that alters the rate of a chemical reaction but is not used up in the reaction.
CLASSES OF DIGESTIVE ENZYMES
i) Amylase: Amylase is an enzyme which splits complex carbohydrates to simpler forms e.g. maltase, sucrose, lactase and ptyalin. Amylase is present in the saliva of humans and mammals where it begins the chemical process of digestion.
ii) Protease: A group of enzymes involves in the breaking down of protein and peptides molecules into constituent amino acids e.g.pepsin, renin, trypsin and erepsin.
iii) Lipases: Lipase is an enzymes which split lipids (fats) to fatty acids and glycerol e.g. steapsin.
CHARACTERISTICS OF DIGESTIVE ENZYMES
i) All enzymes are protein in nature.
ii) Enzymes are catalyst.
iii) Enzymes are very efficient.
iv) Enzymes remain chemically unchanged at the end of a reaction.
v) Enzymes are sensitive to temperature and perform best at optimum temperature.
MODES OF NUTRITION
There are two main modes of nutrition.
1. AUTOTROPHIC NUTRITION: This is a form of nutrition in which the organism makes its own food from simple inorganic substance, such as carbon dioxide and water.
There are two types;
a) Photosynthesis: Photosynthesis is the process by which green plant synthesize their food using water and carbon dioxide in the presence of chlorophyll and sunlight, with the release of oxygen as by-product.
b) Chemosynthesis: Chemosynthesis is the process by which food (glucose) is made by bacteria using chemicals as the energy source, rather than sunlight. Chemosynthesis occurs around hydrothermal vents and methane seeps in the deep sea where sunlight is absent.
2. HETEROTROPHIC NUTRITION: A form of nutrition in which organisms feed on organic substances made by other organisms. Types of heterotrophic nutrition are
i) Holozoic Nutrition: Holozoic nutrition is a type of heterotrophic nutrition that is characterized by the internalization (ingestion) and internal processing of liquids or solid food particles
ii) Parasitic Nutrition: Parasitic nutrition is a mode of heterotrophic nutrition where an organism known as a parasite lives on the body surface or inside the body of another type of organism known as a host. For example, worm living in animals. The parasite does not process it own food but feeds on the food eaten by the animal (the host) thereby depriving the host of nutrients.
iii) Symbiotic Nutrition: The mode of nutrition in which two different organisms live together, share shelter and nutrients is called symbiotic nutrition. In organisms called lichens, alga and a fungus live together. Alga contains chlorophyll and is autotroph, while fungus lacks chlorophyll and is heterotroph.
iv) Saprophytic Nutrition: is a process of chemoheterotrophic extracellular digestion involved in the processing of dead or decayed organic matter. It occurs in saprotrophs or heterotrophs, and is most often associated with fungi (for example Mucor) and soil bacteria.
v) Carnivorous Nutrition in Plants: Carnivorous plants can trap and digest insects and other small animals. Carnivorous plants live in bogs, where nitrates are in short supply, so they need to obtain their nitrogen by digesting prey instead.
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